Field of the Invention
The present invention provides a method of separating a saccharide from an aqueous product solution of the cellulose hydrolysis process, especially a method of separating a saccharide from an aqueous product solution of the cellulose hydrolysis process using a cellulose swelling agent.
Descriptions of the Related Art
Due to the depletion of petroleum reserves, many studies are currently being conducted to develop new energy sources by fermenting saccharides in biomass such as corn stover, corn on the cob, straw, and corn fiber into alcohols. Cellulose, which comprises the majority of biomass, is a polymer of glucose. The cellulose can be hydrolyzed to form monosaccharides or oligosaccharides facilitates, and then fermented into alcohols.
Generally the hydrolysis of cellulose is carried out by mixing the cellulose with acidic aqueous solution and adding a suitable cellulose swelling agent in the obtained mixture. The cellulose swelling agent will facilitate the dissolution of the cellulose in water and increase the hydrolyzing rate of the cellulose. Common cellulose swelling agents include metal chlorides such as zinc chloride, calcium chloride, and magnesium chloride. After the cellulose is hydrolyzed into monosaccharides or oligosaccharides, the saccharides in the aqueous product solution are separated for subsequent processes.
One of the problems in the process of hydrolyzing cellulose into monosaccharides or oligosaccharides using the cellulose swelling agent is the separation of the cellulose swelling agent from the aqueous product solution. Several methods have been proposed for the separation. For example, U.S. Pat. No. 4,452,640 mentions that glucose (the cellulose hydrolysis product) and zinc chloride (the cellulose swelling agent) are difficult to separate, and suggests using ion exclusion with an anion exchanger to separate glucose and zinc chloride from the aqueous product solution. U.S. Pat. No. 4,018,620 employs calcium chloride as a cellulose swelling agent, and the cellulose swelling agent is separated by crystalizing out calcium chloride as a hexahydrate or by adding sulfuric acid into the aqueous product solution to form calcium sulfate precipitate. U.S. Pub. No. 2014/0331992 A1 suggests adding an organic solvent into the aqueous product solution as an anti-solvent to precipitate and separate the saccharides.
However, the conventional methods of separating saccharides from the aqueous product solution require a large quantity of solvent and therefore produce lots of waste liquid, which make the replacement or regeneration of the ion exchange resin more frequent, thereby complicating the process. Therefore, there is a need for a method that can effectively separate saccharides from an aqueous product solution of the cellulose hydrolysis process, save energy, and reduce the amount of waste liquid. In view of this, the present invention provides a method of separating a saccharide from an aqueous product solution of the cellulose hydrolysis process, which can efficiently separate the saccharides from the aqueous product solution and recover the materials added during the process. All of these advantages make the method of the present invention economical.